It is customary for an LED with colored emission to be realized by a correspondingly adapted chip. However, this presents problems in the case of green emission, since established techniques, such as an InGaN chip (blue) or an InGaAlP chip (red) cannot be used on account of lack of efficiency. Instead, special solutions have to be employed. Examples of special solutions of this nature are to be found in EP 584 599, DE 198 06 536 and DE 100 24 924. However, they still have a relatively low efficiency. Moreover, they have a relatively strong temperature drift in the color locus of the emission.
Therefore, green-emitting LEDs based on luminescence conversion LEDs have been developed as an alternative. Examples are to be found in WO 01/89001 and EP 1 150 361. However, it has not hitherto been possible to achieve a higher efficiency than with direct-emitting LEDs. This is because of the phosphors (BAM derivatives and sulfides) which have hitherto been available for this purpose and their excitability.
Phosphors of the oxynitridosilicate type are known per se under the shortened formula MSiON; cf. for example “On new rare-earth doped M—Si—Al—O—N materials”, J. van Krevel, TU Eindhoven 2000, ISBN 90-386-2711-4, Chapter 6. They are doped with Tb. Emission is achieved under excitation by 365 nm or 254 nm.
A new type of phosphor is known from the as yet unpublished EP patent application 02 021 117.8 (Docket 2002P15736). It consists of Eu- or Eu,Mn-coactivated oxynitridosilicate of formula MSi2O2N2 (M=Ca, Sr, Ba).